It is well known that minimally invasive interventions have the benefit of reducing the amount of extraneous tissue that is damaged during diagnostic or surgical procedures. This results in shorter patient recovery time, less discomfort, less deleterious side effects and lower costs of the hospital stay. Nowadays, in general surgery, urology, gynecology and cardiology specialties, there is an increase of the amount of interventions carried out by minimally invasive techniques, such as laparoscopic techniques.
Manual minimally invasive techniques in general, and laparoscopy in particular, put stringent requirements on the surgeon carrying out the operation. The surgeon operates in an uncomfortable and tiring posture, with a limited field of view, reduced dexterity and poor tactile perception. To these problems adds the fact that surgeons often have to carry out several consecutive interventions per day, each intervention lasting e.g. from 30 minutes to several hours. In spite of the inherent difficulties, the trend towards minimally invasive procedures is expected to increase further in the coming years due to an increasing average age of the population and pressure of costs in the medical field.
In laparoscopy for example, surgeons are obviously required to be as precise in his moves as in laparotomy. Manipulating long-shaft instruments with motion dexterity reduced to four degrees of freedom about a fulcrum (pivot point) at the instrument access port (also called trocar), i.e. at the incision in the patient body, is not alleviating their task. Complications arise inter-alia by the fact that the required posture is often tiresome and reduces the already limited perception of interacting forces between instrument and tissues. As a result, motorial capabilities of a surgeon normally decay after 20-30 minutes, such that among others trembling, loss of accuracy and loss of tactile sensitivity occur with the resulting risks for the patient. Therefore, new computer and/or robot assisted technologies, such as Minimally Invasive Robotic Surgery (MIRS), are emerging. These technologies aim at improving efficiency, quality and safety of intervention.
In view of the above, MIRS has known significant development during the last decade. Two representative commercial robotic systems are the system known by the trademark ‘DA VINCI’ developed by Intuitive Surgical Inc., Sunnyvale, Calif. and the system known by the trademark ‘ZEUS’ originally developed by Computer Motion Inc., Goleta, Calif. The system known by the name ‘DA VINCI’ is described among others by Moll et al. in U.S. Pat. Nos. 6,659,939; 6,837,883 and other patent documents of the same assignee. The system known by the name ‘ZEUS’ is described among others by Wang et al. in U.S. Pat. Nos. 6,102,850; 5,855,583; 5,762,458; 5,515,478 and other patent documents assigned to Computer Motion Inc., Goleta, Calif.
These teleoperated robotic systems permit to control surgical interventions either directly from the operation theatre or from a remote site, generally using 2-dimensional or 3-dimensional visual feedback only. In either case, the tiring posture of the surgeon is eliminated. Furthermore, these systems tend to give the surgeon the feeling to work in open conditions, e.g. as in laparotomy, and eliminate the aforementioned tiresome posture.
Currently available teleoperated MIS systems typically do not offer true tactile force feedback (referred to as force feedback below) on the console by means of which the surgeon commands the robot(s). Hence the surgeon lacks a true haptic feeling of the forces exerted onto organs and tissues. With such systems, the surgeon has to rely on visual feedback and on his experience to limit interaction of instruments with the intra-patient environment. In this respect, research work has been done concerning a computer-assisted sensorless force feedback system based on the concept that a computer could reproduce what a surgeon skilled in manual MIS procedures is capable of. In other words, a computer could estimate forces from deformations observed by vision. An example of such attempts is found in: “Force feedback using vision”; Kennedy, C. and Desai, J. P.; International Conference on Advanced Robotics; Coimbra, Portugal, 2003. Such systems have however not yet reach a commercially viable state.
As will be appreciated, accurate force feedback is considered a crucial feature to ensure operation safety and to improve the quality of procedures carried out with machine assisted minimally invasive systems. Therefore, force feedback is believed to be of paramount importance for teleoperated interventions.
At the instrument tip level, force sensing allows for example palpation of organs and tissues, which is highly desirable in diagnostic procedures and for identifying critical areas e.g. with arteries. Other possible enhancements consist in the limitation of stretching tension on sutures and the limitation of exerted forces on tissues according to the type and specific phase of the intervention. In practice, contact forces can be kept below a given threshold by increasing motion scales, stopping the manipulator motion, or increasing force feedback on the master device. Furthermore, force sensing would permit to work intuitively with an instrument that is not in the field of view of the endoscope camera, e.g. when the surgeon assistant holds an organ away from the operation field.
At the access port level, force sensing would be beneficial in order to monitor and consequently reduce forces applied by the instrument at the incision for the access port. These forces are the main cause of incision wear that can lead to loss of abdominal pressure, release of the trocar, and increased intervention time due to the need to recover the situation. These detrimental forces are mainly caused by the inaccurate location of the instrument fulcrum (pivot point), as determined by the system and modified due to variations of intra-abdominal pressure, with respect to the patient incision but also by motion drifts of the (robot) manipulator due to its positioning inaccuracy. In manual interventions, these wearing forces are less pronounced because of the human capability to intuitively adjust hand motion with respect to the optimal pivot point in the incision.
To overcome the trocar-release problem, the aforementioned DA VINCI system for example, uses a trocar attached to the manipulator wrist at the extremity of the instrument insertion/extraction slide. This solution does not reduce the risk the incision wear and does not improve the loss of abdominal pressure.
In order to overcome the latter problem at the trocar level, a force-feedback adaptive controller, which is capable of automatically adjusting the fulcrum point of a robot manipulator on a plane tangent to the abdomen of the patient, has been developed and described in the paper “Achieving High Precision Laparoscopic Manipulation Through Adaptive Force Control”; Krupa, A. Morel, G. De Mathellin M.; Proceedings of the 2002 IEEE Intern. Conference on Robotics and Automation; Washington D.C., May 2002. In this approach, a sensor on the end-effector of a robot in combination with a force controller is used to explicitly regulate the lateral forces exerted onto the trocar, which together with the abdominal wall defines the fulcrum, towards zero. This method and system are not capable of determining the forces at the tip of the instrument inserted through the trocar. Instead, the interaction force at the instrument tip is assumed to be negligible. Therefore, this method can be satisfactorily used only with an endoscope manipulator that does not have any other contact point with the patient.
A different approach is described in the paper: “Development of actuated and sensor integrated forceps for minimally invasive robotic surgery”; B. Kübler, U. Seibold and G. Hirzinger; Jahrestagung der Deutschen Gesellschaft für Computer- and Roboterassistierte Chirurgie (CURAC), October 2004. This paper describes a miniaturized 6DOF force/torque sensor to be installed at the tip of a minimally invasive instrument. This sensor enables accurate sensing of the forces exerted by the instrument tip and corresponding force feedback. This concept has several drawbacks however, among which manufacturing and installation cost, the lack of robustness in autoclave sterilization, and EMI shielding issues when combined with powered instruments. As will be understood, a dedicated sensor has to be provided on every instrument when using this approach. A similar approach has been described in the paper: “A miniature microsurgical instrument tip force sensor for enhanced force feedback during robot-assisted manipulation”; Berkelman, P. J., Whitcomb, L. L., Taylor, R. H., and Jensen, P.; IEEE Transactions on Robotics and Automation, October 2003.
A different approach, which does not require a tip mounted sensor on every instrument has been described in the paper “A New Robot for Force Control in Minimally Invasive Surgery”; Zemiti N., Ortmaier T. et Morel G.; IEEE/RSJ International Conference on Intelligent Robots and Systems, Japan, 2004. This paper describes a robot and force sensor arrangement that can measure the distal organ-instrument interaction with a sensor placed on the trocar. Even though, in this approach, the sensor is not mounted on the instrument itself and is therefore subject to lower miniaturization and sterilization constraints, this solution still requires modified trocars with sensor equipment capable of resisting sterilization. A further approach designed for MIS, as disclosed in patent application WO 2005/039835, uses a master/slave architecture with two PHANTOM® haptic devices developed by SensAble Technologies, Woburn, Mass. This system comprises a first PHANTOM device integrated into a slave subsystem and serving as manipulator for an instrument in combination with an effector sub-assembly that is configured for holding and mounting an off-the shelf instrument tip of a minimally invasive instrument such as graspers, dissectors, scissors, etc. to the first PHANTOM device. In operation, the minimally invasive instrument has a first end mounted to the effector sub-assembly and a second end located beyond an external fulcrum that limits the instrument in motion. In order to provide measurement of the force vector (fx, fy, fz) and the moment (Σz) at the end of the instrument tip, a custom made arrangement of various strain gauges is provided. Furthermore, the system comprises one or more personal computers with application programs for controlling and serving the first PHANTOM device of the slave subsystem and a second PHAMTOM device of the master subsystem.